Method of sealing a cavern having anhydrous ammonia stored therein during removal or insertion of pumping devices



`3,530,674 IA STORED DEVICES T M n J. H. coBBs lET AL A CAVERN HAVING ANHYDROUS AMMON Filed oct. .17, 196s Sept. 29, 1970 METHOD oF SEALING THEREIN DURING REMOVAL 0R INSERTION oF PUMPING /NVE/VTORS, JAMES H. COBBS B), SIDNEY E. sclssoN l v //eafmn,

ATTORNEYS United States Patent O 'ice' 3,530,674 METHOD OF SEALING A CAVERN HAVING ANHYDROUS AMMONIA STORED THEREIN DURING REMOVAL OR INSERTION OF PUMPING DEVICES James H. Cobbs and Sidney E. Scisson, Tulsa, Okla., assignors to Fenix & Scisson, Inc., Tulsa, Okla., a corporation of Oklahoma Filed Oct. 17, 1968, Ser. No. 768,397 Int. Cl. B65g 5/00; E21f 17/16 ABSTRACT OF THE DISCLOSURE This invention relates to a method of removing a structure from a casing communicating with an underground cavern storing anhydrous ammonia, the cavern having a sump therein into which the casing extends. The invention includes introducing Water under pressure into the casing, the water flowing into the cavern sump, opening the casing to permit removal of the structure, the pressure in the cavern forcing the water upwardly within the casing until the hydrostatic weight of the water column in the casing balances the pressure of the cavern, and removing the structure Without escape of gas or fluids from the cavern.

CROSS-REFERENCE This application is not related to any pending United States or foreign patent application.

SUMMARY AND BACKGROUND OF THE INVENTION In recent years the use of underground caverns for storing liquids has become common. Caverns have many advantages over surface storage, including economy of constructure, safety, and temperature stability. Some types of liquids which are stored in caverns are highly volatile and can be removed from the caverns as required by their inherent pressure. Other types of liquids, including anhydrous ammonia, although volatile, frequently require the use of pumps inserted into the cavern for extraction of the lluid at rates which are required by industry. One problem which has existed is that of removing pumps or other similar structures from the casing communicating with underground caverns in which Ianhydrous ammonia is stored. One solution to the problem is the use of blowout preventer type devices as used in the oil industry. Such blowout preventers are aixed to the upper end of the casing above the earths surface. Structures including tubing, pumps, etc., are extracted through the blowout preventers which are arranged to permit the extraction with a minimum escape of the cavern fluid or liquid, the blowout preventer further providing a means of completely closing the casing once the structure is removed. Such devices have several disadvantages. First, they require operators skilled in their use to permit the removal of a pump or other structure. Second, they inevitably permit the escape of some liquid or gas stored in the cavern under pressure. Third, being mechanical devices they are subject to failure. Fourth, lblowout preventers typically utilized resilient sealing elements, such as rubber components, which must periodically be replaced. Fifth, such blowout preventer devices are relatively expensive.

For these reasons it has become highly desirable to provide some means of sealing a casing communicating with an underground cavern utilized to store anhydrous ammonia in such a Way as to prevent the removal and reinsertion of structures such as tubing, pumps, cable 3,530,674 Patented Sept. 29, 1970 suspended test instruments, etc., without permitting escape of liquids or gases It is therefore an object of this inevntion to provide a method of removing a structure from an underground cavern utilized to store anhydrous ammonia.

More particularly, this invention is directed to a method of removing structure, such as a pump, from a closed casing communicating with a lower sump in an underground storage cavern for storing anhydrous ammonia under pressure.

These objetcs as well as further objects o-f the invention will be understood with reference to the description and claims taken in conjunction with the attached drawings.

DESCRIPTION OF THE DRAWING The ligure is a cross-sectional representation of a cavern formed beneath the earths surface as utilized to store anhydrous ammonia including a casing, shown in cross-section, in communication with the cavern, illustrating means for practicing the method of this invention.

DETAILED DESCRIPTION Referring to the drawing, a cavern 10 is shown as formed in the earth. Such cavern may be formed either by mechanically extracting material from the earth to provide the storage area or by solution mining. A vertical shaft 12 extending from the earths surface 14 provides communication with the cavern. Positioned within the vertical shaft 12 is a casing 16 which is sealed to the shaft 12, such as by cement (not shown) so that no escape of liquid or gases from the cavern may occur along the exterior of the casing 16.

Positioned within the casing 16 is a tubular structure 18 which typically includes a pump 20 at the lower end thereof. The pump 20 imay be actuated by a piston rod or rotating shaft within the tubular structure 18 driven by a pump prime mover 22 at the upper end. Another typical arrangement includes a pump 20 of the submersible electrical type which would include a power cable running within the casing 12 and exterior of the tubular structure 18 to the surface.

Casing 16 is closed at the upper end by a closure member 24 which supports and seals the tubular structure 18 and prevents the escape of liquid or gases.

The tubular structure 18 includes a T-titting 26 at the upper end above the closure member 24 receiving a flow line 28 through which products can be extracted from the cavern by means of pump 20.

The casing 16 includes an outlet 30 to which is affixed a check valve 32. The valve in turn is connected to a pump 34 and the pump is connected to a water supply 36.

The casing 16 may also include a second outlet 38 selectably closed by a valve 40 providing means of discharge of gas [from the interior of the casing.

Formed within the lower surface of cavern 10 is a sump 42. Heavier components of liquid or gases within the cavern ow by the force of gravity into sump 42.

The method of the invention will now be described. When it is `desired to remove a structure such as the illustrated string of tubing 18 having pump 20 at the lower end thereof, pump 34 is actuated to pump water from reservoir 36 through check valve 32 into the casing 16. The water flows down within the casing into sump 42. After suicient water is deposited 'within the sump 42 valve 40 may be opened releasing pressure from the interior of the casing 16. As the pressure in the casing is released water is forced by the pressure in the cavern upwardly within the casing until a water column is reached having a hydrostatic head pressure equal to the pressure of fluid within the cavern 10. Once this height of water is attained within casing 16 the column of water will rise no further. At this point the pressure above the water column is equalized through valve 40 and the closure member 24 may then be removed. After removal of closure member 24 the structure 18, including the pump 20, may be removed from the interior of the casing without permitting the escape of any of the liquid or gases contained in the cavern 10. The water 46 functions as a liquid seal preventing the anhydrous ammonia 48 either in liquid or gas form, from llo'wing upwardly through the casing.

After the pump is repaired, replaced or otherwise, it can be reinserted, with tubular structure 18, within the casing 16, again without permitting the escape of liquid or gases. After the tubular structure 18 is in position in the casing 16 the closure member 24 may be placed in position. Valve 40 may then be closed. Pump prime mover 22 may then be energized pumping the water from the sump 42. As the pump is actuated the water in the casing and in the sump 42 ywill first be removed. Such water may be discarded. After the water has been pumped from the interior of the casing and sump 42 further pumping will deliver to flow line 28 the stored product, that is, anhydrous ammonia.

It is generally understood that ammonia is readily soluble in water to become either ammonia hydroxide or ammonia. Ammonia hydroxide occurs as a reaction between anhydrous ammonia and water, whereas aqua ammonia is a result of ammonia being dissolved in the water without reaction. The mixture of anhydrous ammonia and water normally produces a solution containing both ammonia hydroxide and aqua ammonia.

Water is substantially heavier than liquid anhydrous ammonia. At the pressure and temperatures at which anhydrous ammonia is normally stored the specific gravity is .62. Aqua ammonia has specific gravity of approximately .89. Thu-s any mixture of liquid ammonia and water will produce as a product a liquid having a specific gravity somewhere between .62 and .89.

It has been learned that depositing water into a sump in an underground storage cavern utilized to store anhydrous ammonia does not produce the complete reaction and solution of ammonia into the water as would be expected. As long as the water is in an undisturbed state in sump 42 in cavern 10 containing anhydrous ammonia a relatively thin transition zone 44 between the water and anhydrous ammonia occurs. After the formation of the transition zone of the combined ammonia, ammonia hydroxide, aqua ammonia and water any further disbursement or thickening of the transition zone 44 thereafter is very slow. This appears to be contrary to the belief of the industry wherein it has been previously understood that placing water in anhydrous ammonia would immediately result in the substantially complete disbursement of the water into the ammonia.

As shown in the drawing the water 46 is separated in the sump 42 from the anhydrous ammonia 48 stored in the cavern by the relatively thin transition zone 44. This small, relatively thin, transition zone represents a small quantity of ammonia which may be said to be contaminated by water introduced by the method of the invention to permit removal of the pump 20 or other structure from the casing 12. This small quantity of contaminated ammonia may be discarded or, if desired, can be treated for removal of the ammonia content therefrom, such as by fractional distillation. In the normal cavern the ammonia which combines with water to form the transition zone 44 will be of such small quantity as not to justify the expense 0f subsequent extraction.

It is understood that the invention can be practiced in a variety of manners and this is particularly true as relates to the method of injecting and removing water from the cavern. For instance it can be seen that water could be deposited through a tubular structure rather than into the casing itself.

While the invention has been described with a certain degree of particularity it is manifest that many changes can be made in the arrangement of the structure utilized to practice the invention and in the steps of the invention without departing from the spirit and the scope of this disclosure. It is understood that the invention is not limited by the abstract herein, nor the summary, nor the exemplified embodiment, but is limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element or step thereof is entitled.

What is claimed:

1. A method of removing a structure, such as a pump, from a closed casing communicating with a lower sump in an underground storage cavern utilized to store anhydrous ammonia under pressure comprising the steps of:

introducing a preselected quantity of water under pressure into the casing, the water flowing into the cavern sump;

releasing the closure of the casing to permit the removal of the structure, the pressure in the cavern forcing 'water upwardly within the casing, the quantity of water being sufficient that the hydrostatic'weight of water in the casing balances the pressure in the cavern; and

removing the structure without escape of liquid or gases from the cavern.

2. A method of removing and inserting a structure, such as a pump, for repair 'or replacement, from a closed casing communicating with a lower sump in an underground storage cavern utilized to store anhydrous ammonia under pressure comprising the steps of:

introducing a preselected quantity of water under pressure into the casing, the water flowing into the cavern sump; releasing the closure of the casing to permit the removal of the structure, the pressure in the cavern forcing water upwardly within the casing, the quantity of water being suicient that the hydrostatic weight of water in the casing balances the pressure in the cavern; removing the structure without escape of liquid or gases from the cavern; inserting a structure within the casing; sealably closing the casing; and pumping the water from the cavern sump.

References Cited UNITED STATES PATENTS 2,780,070 2/1957 Meade 61-.5 2,901,889 9/1959 Reed 61-.5 3,084,515 4/1963 Dougherty 61-.5

PETER M. CAUN, Primary Examiner 

